The present invention is directed to a fault indicator for a surge arrester. The function of a surge arrester is to protect a power transmission system from overvoltage surges which are typically caused by lightning, switching transients or faults. A typical surge places a high current overvoltage on the power transmission line capable of destroying any equipment which is connected to the power line. Such equipment might be transformers, terminations, underground cables or splices.
To protect this expensive equipment, a surge arrester is placed on the power transmission line near the equipment to be protected. The arrester normally acts as a insulator, allowing essentially no current to pass through it, but an overvoltage on the line will cause the arrester to become conductive. In the conductive state, the arrester will pass the high current surge directly to ground and allow only a small kilovolt surge to continue down the power transmission line. The equipment the arrester is installed to protect is designed to withstand kilovolt surges and so is capable of maintaining its functionality despite exposure to such a surge.
After passage of the overvoltage surge, the surge arrester is designed to return to its non-conductive state and is ready for the next instance of an overvoltage surge. However, it is possible that the magnitude of the overvoltage surge may be such that the surge arrester fails, in which case the surge arrester continues to conduct current even after passage of the surge. Failure of the surge arrester may also be caused by moisture ingress into the surge arrester or contamination of the exterior of the arrester.
The fault indicator of the present invention is designed to provide a visual indication of surge arrester failure so that the faulty surge arrester can be easily identified and appropriate action taken.
A fault indicator must meet three requirements. First, the fault indicator must not alter the behavior characteristics of the surge arrester to which it is attached. Second, if the attached arrester fails, the fault indicator must give a visual signal which is preferably detectable day or night from at least thirty meters. Third, the fault indicator must have the capability of maintaining a phase to ground fault through the faulted surge arrester without failing itself.